EPIDERMAL GROWTH-FACTOR INTERACTS WITH INDOLE-3-ACETIC-ACID AND PROMOTES COLEOPTILE GROWTH

We used coleoptile sections of A vena sativa, Sorghum bicolor, and Zea mays seedlings to examine interactions between epidermal growth facto r (EGF) and indole-3-acetic acid (IAA) that may affect plant growth an d development. Our 24-h bioassays employed three controls ranging in d ilution from 10(-4) to 10(-8) g ml(-1): (1) 50 mM potassium-phosphate buffer solution (pH = 6.0), (2) bovine serum albumin, a nonspecific pr otein; and (3) IAA; plus two treatments: (1) mouse epidermal growth fa ctor (EGF) ranging from 10(-6) to 10(-10) g ml(-1), and (2) EGF+IAA. I n all three species growth in IAA, EGF, and EGF+IAA treatments showed significant increases over controls; EGF+IAA showed significant increa ses in growth over IAA alone. As the concentrations of IAA decreased, the EGF and IAA interaction became more pronounced. At the highest IAA concentrations, EGF+IAA increased growth rates ca. 2% to 39%, whereas at lower IAA concentrations EGF+IAA promoted growth as much as 121%, thereby lowering the normal IAA physiological set point up to three or four orders of magnitude. Our data suggest that an interaction betwee n EGF and IAA may allow plants to recognize and respond to animal bioc hemical messengers, resulting in changes in plant cell elongation that ultimately may alter plant growth patterns.